Process of purifying gases.



H. L. DOHERTY.

PROCESS OF PURIFYING GASES. APPLICATION FILED PEB.15, 1910.

. 1,038,315. Patnted Sept. 10,1912.

2 SfiEETS-SHEET l.

44%oao: Henry LDoh crty, avvuewtoz H. L. DOHERTY.

PROGESS 0P PURIFYING GASES. APPLICATION 31mm rmms, 1910.

1,038,3 1 5, Patentd Sept. 10, 1912.

2 SHEBTBBHEET 2.

i/bwcoaco: Henry Dohe rty, awvcM-toz To all whom it may concern: A

HENRY 1.. nonsarr, orrmw roux, N. r.

rnoonss or rURrrYrne-oasss. I

' Specification of Letters Patent.

rammed Sept. 10, 191a.

. Application filed February 15, 1910. Serial No. 544,093.

Be it known that I, HENRY L. DoHERrY,

' a citizen of the United States, and a resident of New York city, inthe county of New York and State of New York, have invented certain newand useful Improvements in Processesof Purifying Gases, of which thefollowing is a' specification.

This invention relates to' a process for carryin out theself-purification of gases, or, in 0t er words, to a process forpurifying gases which, in their crude state, contain ammonia, byseparating the ammonia from one portion of the gas as ammonia liquor andafter revivifying the liquor using it to.

purify another portion of the gas.

The object of my invention is to furnish a process whereby coal gas,producer gas. etc., ma be urified without the use of any materia s ot erthan materials which are carried by the crude gases themselves, thusdoing away with the, at present, necessary outlay for. extraneouspurifying materials.

Another, but subordinate, object of my invention is the substitution offluid purl v fying agents for solid, whereby the entire handling andcirculation of the materials may be performed by pumps and without anymanual labor.

In the accompanying drawings I have shown, in rather diagrammaticarrangement, 9. form of apparatusgsuitable for carrying out my process.

tributing trays of some sort, adapted 'to.

"F gure 1 1s a diagrammatic elevation of the apparatus used in purifyingthe differ 'ent liquors used in scrubbing the gas. Fig.

2 is a vertical diametral part section through the ammonia liquorpurifyingst-ill, showing the method by which the gases evolved in. thestill are contacted with an op ositel flowin current of li uor. Fig. 3 asii nilar se ztion through ime ofthe boiling chambers of the still.-Fig.4 is a perspective view of the gas washin and cooling apparatus.Fig. 5 is a partia view of the arrangement by which the scrubbing liquidis permit-ted to find its way from one compartment of thewasher-.coolerto the next in series.

in the apparatus shown isas.-follows:'-The foul as to be purified enterscompartment a of t e washer-cooler 1, through the pipe 2. Thecompartments of 1- are, preferably, filled with someform ofgrids, 13, ordispartment in such a manner that it passes downward through thecompartment asa rain or a plurality of film-like streams. In

this way a large extent of liquid surface is exposed to the gas andintimate contact between the gas and liquid secured. The specific scrubing apparatus, which. I prefer to use, and have here shown, is thatcovered by U. S. Letters Patent to me No.

7 however, any other efiicient form of apparatus may be substituted forthis in carryingcut my process.

In the preferredway of carrying out my process, I first subject thegas--say in compartments a, b and ct0 an initlal' scrubbing and coolingby contacting it with coal tar oils. This step is particu larlyapplicable to the purification of illuminating gas break up the liquidfalling through the comand is designed, chiefly, to eliminatenaphthalene, as well as to reduce the gas to a temperature at which thesubsequent scrubbing'wit-h artially purified ammonia liquor becomeseective. The ment at, passes u throug the same, through the "port 4' tote upper part of compartment 6,, through the port 4" to the lower part ofcompartment 0, up through 0, through the port. 4""to the upper part ofcompartment d, and so on through the up .per and lower communicatingports, alternately,':'until it finally dischargesthrough thepipe 6.

In'the arrangement shown, the gas is first contacted with the ammonialiquor in compart-mentd. Here it is scrubbed by the nearly saturatedliquor just before the latter is withdrawn from the washer-coolerthrough the pipe 5. In this compartment the liquor is fully saturatedwith the impurities of the ressure preval ing in compartment (Z.

hesurplus saturated liquor 1s withdrawn front the liquid-collectingcistern at the .80 as enters compartas at the temperature and bottom ofcompartment (5, and flows to the ammonia-1i vuor Y urifying plant, 7.Here it is treate in t e'manner described later,

i I in such a way that it is divided intothree The method of carryingout my process separate currents,- two of which are returned to thewasher-cooler, 1. The main body of liquor is comprised in current A,which conthe free or hydrated condition. (NH or NH- OHM The actualproportion of 'the vtotalammonia, which is present in this curtion,isfrom 50 to 60 per cent. This current A is returned to the cooling coilsof the next to the last compartment of the washercooler-g, in theconstruction shown. After passing through the cooling coil of g, theliquor, enters the distributing device in the upper part of g and thendescends in contact with the nearly purified gas passing' through 9.

Current B 1s composed of liquor from -which substantially all of thevolatilizable ammonia has been driven off. This current passes throughthe cooling coils of the last compartment, h, of the washer-cooler andthence to the-distributing device in the upper-part of h and downthrough h. The gas passing through II. will have had nearly all of itsimpurities eliminated before reaching this compartment. Here the lasttraces of ammonia will be absorbed from the gas by the current B whichenters the compartment h, substantially, free from volatile ammonia.Owing .to the vapor tension possessed by ammonia, even in relativelydilute solutions, current A cannot be used for the removal of the lasttraces of ammonia from the gas. In ordinary gas works practice, this isaccomplished by the use of pure water. 'The use of extraneous water,how.- ever, is objectionable ;in that it necessarily occasions adilution of the ammonia liquor formed. Ordinarily, the amount of water.

formed-is amply sufficient to holdall of the simultaneously-formedammonia in solution, at the temperature at which the gas is discharging1IEI'OII1 the scrubbing apparatus. Owing, however, to the vapor'tensionof the ammonia, the automatically-formed ammonia liquor cannotremove'the last traces of gaseous ammonia from the gas. By my method ofremoving substantially all of the volatile ammonia from-a portion of thegas liquor and using the so-treated liquor to remove the last traces ofammonia from the gas, I am'able to secure the same results as when usingfresh water for the final scrubbing and, therebypavoid the dilution ofthe liquor formed.

The liquor does not, simply flow directly through the differentcompartments of the washer-cooler in a stream of uniform volume, butthere is maintained in circulation in each compartment a body of liquormuch greater than the quantity flowing from one compartment to the next.Each compart: menthas a special circulating pump, the

pumps being numbered 8., 8 8,, etc., the subscript denoting thecompartment to which each pump is connected. Suction pipes, 9 9 9 etc.,connect the respective the corresponding compartment. Discharge pipe'1010 10,, etc., conduct the discharge from the several pumps to therespective cooling coils 11 11 11,, etc. From the cooling coils theliquor is discharged upon perforated trays 12 12 12,, etc., or otherequivalent distributing devices. From these, I it falls in a greatnumber of fine streams uniformly distributed across the horizontalsection of .the compartment, onto the grids 13 (or equivalent device).The liquid flows down through the compartment from grid to gridabsorbing the impurities of the gas and drips from ithe' last grid ontothe splash-boards 14, from which the liquid flows quietly to therespective cisterns (3,, (3 6 etc. From these it is again drawn by thepumps 8,, 8 8,, etc., and raised to the respective cooling coils 11 1111 etc., to again pass down through the corresponding compartment. Asthe volume of the liquid circulating in the compartments 9 and h isincreased by currents B and A, a volume of liquid corresponding to theincrement received flows. from one compartment to the next through theconnecting seal, finally reaching the liquid-collecting-cistern (3. Theflow from chamber to chamber is also increased by the condensation fromthe gas. The liquid seal device between the chambers consists, simply,of two-plates, 16,, and 16 forming dams in the compartments h and g,respectively, and spaced a few inches from the wall dividing thecompartments. Apertures '17, in the dividing Wall below the tops of thedams, permit the excess liquid to pass from compartment 71. to.compartment 9. A similar seal permits the liquid to pass fromcompartment 9 to compartment f, and so on to the compartment (2. Fromthis compartment, the liquor is withdrawn and led to the ammoniapurifying plant to be regenerated.

The saturated liquor (or in as nearly saturated a condition asv can beobtained) is pumped by the pump 8, to the heater-cooler 19 through thepipe 5. 19 may be of any suitable construction which will provide forthe transference of heat from the two currents of hot purified liquor tothe cold saturated liquor. In the apparatus shown it is a common type oftubular heater having a lower and an upper tube sheet, 20 and 20,respectively, whlch sheets support a plurahty of tubes through which thetwo chambers, 21, 21, are in communication. A partition, 22, divides theinter-tubular part of 19; into two chambers, 23, 23. The cold saturated,or foul, liquor from the gas washer-cooler 1, enters the chamber 21 of19, passes up through the tubes (not shown) -to the chamber 21' andthence flows to the "still 25. During its ascension through the tubes of19 the foul liquor is subjected to heating by the two currents of hotpurified pumpswith the liquid-collecting cistern of about 98 and 124Fah.,, respectively.v Therefore the preliminary heating to which thefoul liquor is subjected in 19 causesthe made up'of three heatingBreaking up of a portion of the ammonium sulfid and carbonaterespectively with the evolution of a considerable volume of H 8 and 00These evolved gases pass through the vapor pipe 24 to one of thesections of still 25. The heated foul liquor discharges from 19 throughthe pipe 26v to one of the sections of '25. This ammonia-purifying still25 is preferably constructed as follows The lower or retort portion ofthe still is chambers or retorts, 27, 27 and 27 with a seal section, 28,interposed between the retorts 27 and27". The retorts 27" and 27", aresimply open chambers provided with heating 0011s 29 and 29,respectively. A by-pass, 30, establishes communication between the vaporspaces of the respective retorts. passages, 31,-31', 31", provide forthe passa e of liquor from 27 to 28, 27 to 27', and 27 to 27respectively. The retort 27 is constructed as shownin Fig. 3. Throughthe bottom of 27 projects a vapor passage 32. In the bottom of 27 is asteam coil'29.

Covering the endof 32 is a hood33, imper foratein its dome-shapedportion but with perforations, 34, in its flange ortion. A

,. ring cast onto the periphery o the flange .of 33 (not shown) supports33 at the proper height above the bottom of the retort. The upperorifice of overflow 31 is arranged to be at the height above theperforated flange 33 at which it is desi ned to maintain the liquid in27. The sectlon 28, has no heating 0011 but is,-otherwise, similar indesign to 27. In its bottom is a rojecting vapor passage 35, covered bya mod 36, imperforate as to its dome portion but having perforations',37, in its flange portion. The vapors from 27 pass through the passage35 under hood 36 and thence through the perforations 37 into the vaporspace of 28, from which they pass through 32, thence through theperforations 34 and bubble through the liquor in 27, thence into thesection 38'. The sect-ions 38 are built onto retort 27 and are identicalin construction to section .28, except that they areprovided withoverflow passages 35'. The hot foul liquor enters one of theintermediate sections of the 'Stlll (38 as shown). The section at whichit may be entered into the still may be varied but, preferably, it isentered into that section in which the foul gases passing through thesection have a temperature slightly higher than that of thetfoul liquor.The

25. In passing up through the sections section being, at the same time,contacted with the current of hot foul gases passin upward from theretort sections of the stil the hot gases give up part of their sensibleto the descending liquor. This latter is heat I radually raised'lntemperature and has a urther portion of its ammonium sulfid and ammoniumcarbonate dissociated, with the evolution of more H 8 and CO Owing tothe fact that the solubility of H,S and CO diminishes with the rise intemperature very much more rapidly than does the solubility of theammonia, substantially all of these gases, that are freed from theirammonia combinations, are immediately evolved from the li' uor while, onthe other hand, nearly all 0 theiammonia, liberated from combination, isretained in the liquor as free or hydrated ammonia. In addition, theliquor descending through the sections 38, picks up part of the,ammonia, which is present with the foul gases, having been driven offfrom the liquor in the retortsections of the still. R 1

When the liquor has reached retort 27, it has already assumed afairlyhigh temperature. The dissociation of the ammonium salts of the foulliquor in the heater-cooler and in the sections of still 25 throughwhich it flows, before reaching the compartment 27, causes theabsorption of a considerable quantity of heat. This heat is en plied, inthe case of the heater-cooler, by hot purified liquor from 27 and, inthe cas of the still, by the hot vapors and gases from 27. The heatrecuperation is thusgreatly facilitated, and the capacity of the twopieces of apparatus increased in proportion to the heat so-renderedlatent. In 27, by means of the steam coil 29, the temperature of the,partially water under the pressure prevailing in- 27. The exacttemperature I use depends upon the pressure conditions in 27 This deends, of course, upon the'altitude of-the loca ity in which thetreatment is carried out and upon the back pressure caused by the li uidseals in the compartments of the still. 1 s stated, I prefer to carry onthe treatment in compartment 27 at a. temperature varying from 6 to 12degreesbelow the boiling temperature under the pressure prevailing in27. For example, ifsthe barometric pressure in 27 is about 25.9 inchesof mercury, I would preferably maintain the tem erature in 27 at about197 to 198 Fah., w ile at a barometric pressure of sa compartment 27 Iwon d preferablyheat the liquor therein at a temperature of about 204 to206 FahJ While. purification can be effected. considerabl below thistemperature,

31.3 inches in. the.

not consider it advisable to use temperatures lower than that given,although the separation of the foul gases and the ammonia may be,thereby, made with less loss -.of ammonia in the one operation. At thisrange of temperature, 197 to 204, the decomposition of the ammoniumsulfid and carbonate is very rapid. The freed foul gases pass off veryrapidly from the liquor, setting up' a pseudo ebullition. A portion ofthe NH also passes off with the foul gases, the carrying off of theammonia being, in part,

mechanical. That is to say, the foul gases,

so to speak, entangle a portion of the ammonia freed in the bubbleswhich they form and prevent it coming into sufliciently intimate contactwiththe liquor to permit of its absorption by the latter. For thisreason, were the treatment in retort 27 depended upon for thepurification of'the main stream of liquor, the latter would never besecured in the Condition of saturation at the temperature prevailing in27 By the device which I use, however, of passing a current of gasesstronger in ammonia, which is formed in the retorts 27 and 27 throughthat portion of the purified liquor which is returned to compartment 9of the washercooler, I am able to withdraw this current of liquor fromthe still, through the pipe 39, practically saturated with NH at thetemperature which it possesses in 28 The partially purified liquordischarging from 27 is divided into two currents: The

main current, which I designate as current A, passes through theoverflow 31 into the section '28. The other current passes through theconnection 31', having a valve 31 into the retort 27.'- Here, it issubjected to active boiling until nearly all of its volatilizableammonia has been driven off. The liquor, freed from most of itsvolatilizable ammonia and acid constituents, discharging from 27' issub-divided into'two portions the main current being withdrawn throughthe pipe 40, while the minor current passes tort 27".

through the overflow 31. into the liming re- As it discharges from theoverflow 31 it mingles with a stream of milkof lime liquor in, 2-8, aportion of the NH, of the gases belng absorbed by the liquor in 28. Ifprefgrred, the ammonia liberated in 27 may be led oflF' through a pipe41 and used to form a fairly pure ammonia ii uor. The liquor withdrawnfrom 27 which should have been deprived of substantially all of itsammonia, is run to waste through the pi e 42.

The partially purified liquor drawn off from 28 through the pipe 39, isforced by pump 42 to the larger mtertubular compartment 23 ofheater-cooler 19. In assing through 23, it is cooled by the co d foulliquor passing through the tubes of 19, and discharging from 23 passesthrough the pipe l5 to the circulating pump 8 of compartment 9 ofwasher-cooler 1. The ortion of the liquor, freed from substantia 1y allof' its volatilizable ammonia, which is withdrawn from 27 through thepipe'40, passes to the pump 43, and 1S forced, thereby, to

the upper part of intertubular compartment 23 of heater-cooler 19. Itpasses down through 23 and discharges through 44 to the pump 45. Theliquor discharging from 45, is subdivided into two streams'-the largerstream passing through the pipe 15 to the circulating pump ofcompartment h, thence, with the body of liquor in circulation in IL,through the cooling coil 11 ,and into the gas chamber h, where it isused to remove the last traces of ammonia from the gas as alreadydescribed. The smaller stream of the liquor, substantially free fromvolatilizable gases, passes through the pipe 44 to the cooling coil 46.46 is cooled by cold water dripping over it from the distributing trough47 or in any other preferred manner. The cold liquor of this lastmentioned stream, discharges into the 'uppermost section of still 25,and overflows from section to section until it reaches (in thearrangement shown) the section 38 During its descent through thesections, it is contacted with the foul gases passing upward through thestill, and absorbs from them the last traces of the ammonia which theycarry and also ortions of the fouling gases themselves, w ich portionsof the gases re-combine with the ammonia as the temperature falls andpass, with the ammonia, into the liquor. From section 38 (or any otherone above the one into which 26 is connected, that I refer) I withdrawall, or a portion, of t is current of liquor through the pipe 49,having1 and conduct it to storage, or ispose of it in any advantageousmanner. I aim to so regulate the operations that I draw off through 49 aportion of liquor which, with that dis charging through 42, will equalthe increment of liquid received by the system, and will carry aproportion of ammonia corresponding, approximately, to the ammoniaincrement received by the system. It is necessary to enter into theupper section (38 as shown) sufiicient cold liquor, free fromvolatilizable ammonia, to re-absorb all the 'ammonia in the foul gases.Any excess liquor over that which I wish to witha valve 49',

allowed to waste, or be treated as desired.

While it is advantageous to have the liquor, withdrawn through 39,contain the' highest proportion of its ammonia, practicable, in the freeor hydrated condition, I find that, practically, aliquor containing from50 to of itsv ammonia in the free,

condition will meet all requirements in the second scrubbing of the gasv in washercooler 1,, The proportions of the hydrogen sulfid and carbondioxid eliminated from the foul liquor in its passage through the still25 to pipe 39 is about 55 to in each case. At the same timeI aim toeliminate from the liquor a proportion of its ammonia that correspondsto the ammonia increment of the system. The proportion of the ammoniaeliminated may be controlled by varying thetemperature to which theliquor is subjected in 27. Usually, the proportion of ammonia eliminatedwill be between 5 and 10% of the total ammonia in the liquor.

As previously ex lained, the compartments at, b and c, in he arrangementshown, are used for the first scrubbingof the gas.- This is referablydone with coaltar oils recovered from a previously treated'portion' ofthe gas. By this treatment, I' am able to cool the gas down to atemperature at which the ammonia scrubbing becomes effective, say, below120. Fah. -In (a) I prefer to use hot tar oils, while in b and a the.

tar oil. is cooled by the coils shown sufiiciently toreduce thetemperature of the gas assing into d down to the point given. ythe tar,washing, I am able to remove the bulk of the naphthalene from the gas.

Having described my invention, what I claim is: I

1. The process of purifying foul gas which comprises, scrubbing said gaswith ammonia liquor containing a substantial proportion of hydratedammonia,whereby acid impurities in said gas are taken into combinationby said hydrated ammonia, withdrawing the ammonia liquor from contactwith said gas, separating from said.

liquor the major portion of its acid constituents while retaining insaid liquor the major portion of its ammonia, by heating said liquor,whereby-hydrated ammonia is regenerated in said liquor, and re-usingsaid regenerated liquor to scrub another portion of said foul gas. i

2. The process of purifying foul gas which comprises, scrubbing said gaswith ammonia liquorcontaining a substantial proportion of hydratedammonia, whereby acid impurities in said gas, are taken into combinationby said. hydrated ammonia,

withdrawing the ammonia li uor from contact with said gas, regeneratingsaid liquor by heating the same to separate therefrom the major portionof its acid constituents while retaining therein the major portion ofits ammonia, separating the regenerated liquor into two streams,scrubbing a fresh portion of foul gas with the liquor in one ofthesestreams, subjecting the other of these streams to heating to free itfrom substantially all'of its volatilizable gases, and subjecting thegas scrubbed by the first of the said streams to further scrubbing bythe ;other of said streams after the same has been freed from itsvolatilizable gases.

3'. The process of purifying foul gas which comprises, scrubbing saidgas with ammonia liquor containing a substantial proportion of hydratedammonia, whereby acid impurities in said gas are taken into combinationby: said hydrated ammonia,

. withdrawing the ammonia liquor from contact with said gas.regenerating said liquor by heating the same to separate therefrom themajor portion of its acid constituents while retaining therein the majorportion of its ammonia,dividing the regenerated liquor into twoportions, scrubbing another body of foul gas with a portion of saidregenerated liquor, heating the other portion of the regenerated liquorto eliminate volatilizable gases therefrom, subdividing the liquor fromwhich volatilizable gases have been eliminated into two streams, usingone of these streams to re-absorb the ammonia separated from saidliquorwith said acid gases, and the other of said streams to scrub thegas after the same has been scrubbed by the first-treated liquid.

1 4. The process of purifying foul coal gas by substances obtained fromthe said gas,

which comprises scrubbing the foul gas successively'by two portions oftreated liquid condensation from a previously made volume of said gas,the first portion of said liquid condensation having been treated tofree it from the major part of its acid constituents, the other portionof said liquid condensation having been treated to free it from,substantially, all of its volatilizable gases, and withdrawing from thesystem the surplus ammonia and liquid by treating another portion ofliquid condensation to free volume of gas, heating the liquidcondensation containing the fouling constituents at a temperature below200 Fah., whereby the major portion of the-CO and H s contained in theliquid condensation is elimified, while the major portion of the ammoniais retained therein, cooling a portion ofthe so-purified liquidcondensation and using it to absorb the fouling constituents from afresh portion of foul gas, subjecting the remaining portion of theso-heated liquid to boiling to eliminate therefrom the volatilizableammonia, subdividing this portion of liquid intotwo streams, using oneof these streams to absorb the ammonia from the gases evolved from thesaid liquid condensation on-heating, and using the other of thesestreams to absorb the final portion of the ammonia from said coal gasafter it has been scrubbed by said purified. liquid.

6. The process of purifying foul gas which comprises contacting said gaswith a liquor containing free ammonia, whereby the ammonia and otherimpurities of said gas are absorbed in said liquor and said liquorfouled,, withdrawing said liquor from contact with said gas, subjectingsaid liquor to heating, whereby part of theammonia, hydrogen sulfid andcarbon dioxid held by said liquor is evolved therefrom, and the saidliquor purified, dividing the said purified liquor into two portions,cooling one of these portions'and contacting it with a fresh volume offoul gas, subjecting the other portion of saidpurified liquor to boilingto drive off from said portion of liquor,

substantially, all of its volatilizable ammonia, subdividing saidportion of liquor into two streams, usingone of these streams to absorbthe, ammonia from the gases evolved in the heating of said fouled liquorand contacting the other stream of said liquor, freed from substantiallyallof its volatilizable ammonia, with said fresh volume of foul gasafter the same purified liquor. I

7. The process of purifying foul gas which comprises contacting saidgas'with liquor containing free ammonia, whereby the major portion ofthe ammonia and other impurities of said gas are absorbed in said liquorand said liquor fouled, withdrawing said foul'liquor from cont-act withsaid gas, subjecting said foul liquor to a preliminary heating by acurrent of purified liquor,

whereby said purified liquor is cooled, further heating saidfoul liquorto a tempera 'ture above the dissociation temperature of its containedammonium carbonate but below its boiling temperature, whereby the majorportion of the hydrogen sulfid and carbon dioxid of said foul liquor isevolved therefrom and said liquor'purified, dividing said purifiedliquor into two portions, cooling one of these portions, by a freshportion of foul liquor, and contacting said cooled portion of purifiedliquorwi'tha fresh volume of foul gas, subjecting the other portion ofsaid purified liquor to a boiling temperahas been contacted with saidture, whereby substantially all of its volatilizable ammonia is evolvedtherefrom, conducting the evolved ammonia into a fresh portion ofpurified liquor, subdividing the boiled liquor, freed from substantiallyall of its volatilizable ammonia into two streams, cooling one of thesestreams by a fresh portion of foul liquor, subdividing said stream ofcooled liquor into two portions, contacting one of these portions withthe gases evolved in the heating of another portion of foul liquor torecover the contained ammonia therefrom, contacting the other portion ofsaid liquor with a fresh portion of foul gas after the latter has beencontacted with said portion of purified liquor, whereby said gas isfreed from substantially 'all of its impurities, subjecting the other ofthese streams of purified liquor, freed from its volatilizable ammonia,to boiling with lime, whereby the fixed ammonium salts in said portionof liqnor are dissociated andtheir ammonia evolved, and passing theso-evolved ammonia into a fresh portion of purified liquor.

'8. The process of urifying foul gas which comprises scrub ing sald foulgas with liquor containing free ammonia, whereby the free ammonia insaid liquor is saturated with the fouling constituents of the gas,withdrawing said saturated liquor from contact with said foul gas,subjecting said saturated liquor to heating by a current of hot purifiedliquor, further heating said saturated liquor by contact-ing. the samewith the hot gases evolved in the purification of a previous portion ofsaturated liquor, purifging the so-heated liquor by subjecting t e sameto a temperature of between 190 and 200 Fah., whereby the major portionof the hydrogen sulfid and the major portion of the carbon dioxid ofsaid liquor are evolved therefrom together with a relatively smallproportion o the ammonia content of said liquor, whereby a substantialproportion of the ammonia content of said liquor is reconverted to freeor hydrated ammonia, dividing the so-purified liquor into two streams,cooling one of these streams by transferrin its heat to a fresh portionof saturated liquor and contacting the cooled purified liquor with afresh portion of foul gas, subjecting the other portion of said purifiedliquor to boilin whereby substan-- tially all of its volati izableammonia is evolved therefrom, conducting the evolved ammonia into a"fresh portion of purified liquor, subdividing the boiled liquor freedfrom substantially all of its volatillzable ammonia into three parts,the volume of the first of these parts being equal to that required tore-absorb the ammonia content of the gases evolved in the heating of thesaturated liquor, and the volume of the second of these parts beingapproximately equal to the difference in volume of the liquidconpurified liquor freed from-substantially all of its volatilizableammonia and contacting the same with a fresh portion of foul gas afterthe latter has been scrubbed by said urified liquor.

9. The process of purifying foul gas which comprises heating the liquidcondensed from a previously formed portion of said gas to separate fromsaid liquid the major portion of its acid constituents while retainingin said liquid-the major portion of its ammonia, whereby a substantialproportion of the ammonia of said liquid is converted into free orhydrated ammonia,

withdrawing from the body of condensed liquid the proportion of ammoniaand liquid corresponding to the increments of said substances receivedby said body of liquid from said gas, and scrubbing a fresh portion offoul'gas by the residual treated liquid.

10. The process of purifying foul gas which comprises scrubbing said gaswith an ammoniacal liquor containing a substantial proportion of itsammonia in the free or hydrated condition, whereby the major portion ofthe previously free ammonia is saturated with the acid gases of saidfoul gas, withdrawing the said saturated liquor from contact with thescrubbed gas, re-convert-' ing a substantial proportion of the ammoniaof said saturated liquid into the free or hydrated condition by heatingthe same at a temperature above the dissociation temperature of itscontained ammonium carbonate but below the boiling temperature of saidliquor, cooling the major portion of said purified liquor and contactingit with a fresh portion of foul gas, subjecting the-minor portion ofsaid purified liquor to boilingto eliminate therefrom substantially allof its volatilizable' ammonia, conducting the sovola tilized ammoniainto a fresh portion of liquor while the same is undergoingpurificatifin to increase the proportion of free ammonia therein, andcontinuously withdrawing from the body of liquor in circulation a volumeof liquor and ammonia substantially equal to the increments of saidsubstances received by said liquor from said foul gas.

11. The process of purifying foul gas which comprises contacting saidgas first, with coal tar oils derived from a previously treated portionof foul gas, second, with a liquor containing a substantial proportionof free or hydrated ammonia, said liquor being derived from the partialpurification of ammonia liquor derived from a previously treated portionof said foul gas, and third,

with a liquor substantially free from volatilizable ammonia, said liquorsubstantially free from volatilizable ammonia being derived from thetreatment of a portion of said liquor containing a substantialproportion of free or hydrated ammonia.

12. The process of purifying foul gas which comprises contacting saidgas first, with a suitable cooling liquid whereby the temperature ofsaid foul gas is reduced to a temperature below 124 Fah., second, with aliquor containing a substantial proportion of free or hydrated ammonia,said liquor being derived from the partial purification of ammonialiquor condensed from a previously treated'portion of'said foul gas, andthird, with a liquor. substantially free from volatilizable ammonia,said liquor substantially free from vol'atilizable ammonia being derivedfrom the treatment of a portion of said liquor containing a substantialpropor: tion of free or hydrated ammonia.

13. The processof purifying foul gas which comprises cont-acting saidgas first, with a substance capable of absorbing naphthalene, second,with a liquor containing a substantial proportion of free or hydratedammonia, said liquor being derived from the partial purification ofammonia liquor condensed from a previously treated portion of said foulgas, and, third, with a liquor substantiallyfree from volatilizableammonia,

said liquor substantially free from volatilizable ammonia being derivedfrom the treatment *of a portion of said liquor containing a substantialproportion of free or hydrated ammonia.

14'. The process of purifying foul gas which comprises contacting saidgas first, with a cooling liquid which is at the same time capable ofabsorbing naphthalene, whereby the said gas is reduced to a temperaturebelow 124 Fah. and freed from the major portion of its naphthalene,second, with a liquor containing a substantial proortion of free orhydrated ammonia, said proportion of free .or hydrated ammonia.

15. The process ofpurifying foul gas which comprises contacting'saidgas, first, with a cooling liquid which is at the same time capable ofabsorbing naphthalene, whereby the said gas is reduced to a temperaturebelow 124 Fah., and freed from 130 if'quor being derived from thepartial purithe major portion of its naphthalene, second, with a liquorcontaining a 'roportion of free or hydrated ammonia su cient to combinewith substantially all of the-hydrogen sulfid I and carbon-dioxid ofsaid foul gas, whereby nearly all of said impurities are re- .moved fromsaid gas, and third, with a said gas, whereby the said foul gasisreduced to a temperature of, at least, 124 Fah., and the major portionof the naphthaleneis removed therefrom, second, with an ammoniacalliquor containing a substantial proportion of its ammonia in the free orhydrated condition, whereby the major portion of the previously freeammonia in said liquor is saturated with the acid gases of said foulgas, withdrawin the said saturated liquor from contact with the scrubbedgas,

re-converting a substantial pro ortion of the ammonia of said saturatediquor into the free or hydrated condition by heating the same at atemperature above the dissociation temperature of its contained ammoniumcarbonate, but below the boiling temperature of said liquor, cooling themajor portion of said purified liquor and contacting it with a freshportion of foul gas, subjecting the minor portion of said purifiedliquor to boiling to eliminate therefrom, substantially all of itsvolatilizable ammonia, conducting the so-volatilized ammonia into afresh portion of liquor while the same is undergoing purification toincrease the proportion of free ammonia therein, and continuouslywithdrawing from the body of liquor in circulation a volume of liquorand ammonia, substantially equal to the increments of saidsubstances'received by said .liquor from'said foul gas.

Signed at New York city in the county of New York and State of New Yorkthis 12th day of Feb. A. D. 1910. a

' HENRY L. DOHERTY. Witnesses:

L. G. COLEMAN,

THOS. CARTER.

